Nightmare Freeze

In my head canon, Nightmare Moon was an ancient Equestrian ruler who was killed in a coup d'état headed by the invading The Night dynasty in the neighboring Crystal Empire. Legend had it that her reign of terror was so powerful that she would rise from the grave in 1,000 years to regain her control. She did so according to legend and possessed Luna --twice-- and her attempts to regain control failed. The The Night dynasty rules over Equestria today, although the Love dynasty, who rules over the Crystal Empire, is now separate from the The Night dynasty.